What really happens when you put expired sunscreen on your skin

Of course, the day it's unexpectedly bright and sunny would be the day you forgot your sunscreen — just like rain showers always seem to happen when you don't have an umbrella handy. The end result is that you end up owning as many half-used bottles of sunblock as you do umbrellas. While an extra umbrella is never a bad thing — keep one in your bag, stash one in your desk at work, or give one to a neighbor — that sunscreen does have an expiration date. Sunscreens are required by the Food and Drug Administration to remain at their labeled strength for three years, and after that, there's no guarantee they'll work at all (via the Mayo Clinic). So what happens when you slather on on sunblock you remember buying before TikTok was invented? 

"If you use sunscreen after the expiration date, it might still have some UV-blocking power, but it won't be the full strength that's listed on the label," John G. Zampella, M.D. told SELF. He explained that the lotion's sun protection factor, or SPF, will drop in value as time goes by — although there's no real way to tell if your SPF 75 one year after expiration protects your skin at 70 times the rate of no sunscreen at all — or only five times the rate. If the bottle was left out in direct sunlight, it's more likely to be useless. In either case, you're better off buying a brand new bottle.

Expired sunscreen is still better than no sunscreen at all

If you're debating whether to use expired sunscreen or buy a new one, you absolutely should pony up and get a fresh bottle. But here's a different scenario — you're at the beach, you pull out the sunblock at the bottom of your bag, and in the clear light of day, you notice that the expiration date on the bottle has long-past, and there's not a store in sight. Should you use this sunscreen, even though it's probably not as powerful as the SPF on the label claims, or just skip sunscreen altogether?

Definitely use the expired sunscreen in this situation, dermatologists urge. "Expired sunscreen may be better than no sunscreen, especially if the active ingredient is a physical sunblock like zinc oxide or titanium dioxide," Dr. Lauren Ploch told Live Science. Still, Ploch struggled with the idea of sunbathers covering themselves in old, possibly useless sunscreen. "I recommend borrowing sunscreen from someone else on the beach," she urged. In the event of being stranded with questionably effective sunscreen — or worse, no sunscreen at all — Ploch urged covering your skin in clothing. If you can find something made from fabric that's specifically made to screen out ultraviolet rays, all the better, she said.